To date, it has generally been assumed that most contemporary uses of Spanishestar &#8216;be.loc&#8217; arose some time after the use of ser &#8216;be&#8217;, and that the former eventuallytook over most uses of the latter. Previous analyses of diachronic changein estar claim that the usage of this verb became generalized as a result of somereanalysis or grammaticalization change, presumably taking over the resultstate and locative uses of ser. In this paper we wish to go one step further andinvestigate the questions of how adjectival passive estar + participle emerged inSpanish and how it extended its usage at the expense of ser based on an empiricalanalysis of data coming from a large corpus of Spanish texts from the 12th tothe 20th century. We propose that the first and most frequent usesof estar determined the way the participial construction emerged and furtherextended itself, gradually usurping uses of ser, and that the language changemechanism which drove this development was analogy. More specifically, weargue that this development was driven by the analogical relations establishedbetween participles appearing with this verb and locative prepositional phrases.